The Saimiri Monkey as an Experimental Host for the Virus of Yellow Fever

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  • Villavicencio Field Laboratory, Villavicencio, Colombia


The Villavicencio population of Saimiri sciureus caquetensis is highly susceptible to the virus of yellow fever: nineteen animals with negative preinoculation protection tests have been inoculated with known virus, and circulating virus has been recovered in all except one case (an animal that may have received a mixture of virus and antibodies). The maximum titer of virus in circulation is usually at least 1:100,000 and in acute infections exceeds 1:1,000,000.

The mortality rate in a series of fourteen infections with various strains of virus was about 33 per cent. There are usually some pathological changes in the liver in fatal infections, but lesions characteristic of yellow fever as found in man and rhesus monkeys have only been seen in one case. There is usually a clear febrile reaction to the infection.

The species may be infected by doses of virus too small to be detected by the standard method of intracerebral inoculation in susceptible white mice.

Antibody production, as measured by the intracerebral protection test, may be very weak, corresponding to a dilution of 1:64 of immune rhesus serum. There is, however, no evidence of “false positive” reactions.

The advantages of saimiri for the laboratory study of yellow fever virus are: availability (over much of South America), susceptibility, and the relative ease with which the animals can be maintained in captivity.

Disadvantages are: small size, high degree of helminth parasitism, toxicity of pure serum for white mice, and the uncertainty of working with animals that may have been exposed to infection in the wild state before capture.